Valves typically employ a resilient seating material, such as an o-ring, about the perimeter of a port or aperture. The resilient seating material is intended to engage and be compressed by a movable valve sealing member to effect sealing of the port or aperture. The seating material is disposed and contained within a sealing gland, provided in the body of the valve. In order to achieve desirable sealing properties, the seating material must be sealingly engaged to the sealing gland both upstream and downstream of the point of sealing engagement between the valve sealing member and the seating material. Under some operating conditions, the seating member moves away from the sealing gland, creating a flow path, allowing fluid to leak through the port or aperture even though the valve sealing member is sealingly engaged to the seating material. Under these circumstances, sealing engagement of the valve sealing member to the seating material is ineffective in sealing the port or aperture.
To mitigate this problem, it is known to pressurize the cavity within the sealing gland, to thereby provide fluid pressure forces to act upon the seating material, opposing those fluid pressure forces acting on the seating material from within the fluid passage, and thereby mitigating loss of sealing engagement between the seating material and the sealing gland. An example of such a pressurized seal is disclosed in U.S. Pat. No. 5,474,104.
Valves with pressurized seals continue to experience problems with maintaining sealing engagement of the seating surface against the sealing gland. Because the seating surface is pressed into the cavity of the sealing gland, the seating surface is sealingly engaged to the sealing gland at multiple points, thereby creating multiple individual cavities between the seating surface and the sealing gland. It is believed that fluid introduced into the sealing gland, for purposes of pressurizing the seal, does not access these individual cavities. As a result, fluid pressure introduced into the sealing gland cavity is not necessarily effective in opposing the fluid pressure forces acting on the seating member from within the fluid passage, thereby potentially compromising the sealing of the seating member to the sealing gland.